The need for automated inspection of semiconductor components and manufactured parts has been growing rapidly in recent decades. A typical method uses a charge-coupled device (“CCD”) to capture two images of the device that is measured. One image provides planar two-dimensional information of the device, and another image provides height information of the device.
One conventional approach for automated three-dimensional inspection is described in U.S. Pat. No. 6,509,559 entitled, “Binary Optical Grating and Method for Generating a Moire Pattern for 3D imaging”. The invention provides a binary grating in a projection system to generate patterned light, and a three-dimensional imaging system images the patterned light projected onto a surface in order to measure a profile of the surface. The grating includes a binary grating having a cyclical or sine-wave pattern, wherein each cycle includes alternating stripes of varying widths which are substantially clear or substantially opaque.
For such apparatus, the measurement speed depends on the size of a field of view (“FOV”) in each image that is captured. A larger FOV can cover a larger area in each captured image and therefore minimizes the number of images that is required to cover the entire semiconductor tray.
However, increasing the inspection speed can be achieved by increasing the size of FOV, but it will be an expensive approach if height measurement accuracy is not to be sacrificed. That is because it requires a larger CCD sensor, optical lenses with larger diameters, larger size of the whole inspection module as well as larger supports for this module in the machine, all of which lead to prohibitive increases in cost.